全文获取类型
收费全文 | 92502篇 |
免费 | 8538篇 |
国内免费 | 43篇 |
出版年
2023年 | 251篇 |
2022年 | 647篇 |
2021年 | 1625篇 |
2020年 | 923篇 |
2019年 | 1156篇 |
2018年 | 1491篇 |
2017年 | 1285篇 |
2016年 | 2238篇 |
2015年 | 3792篇 |
2014年 | 4222篇 |
2013年 | 5067篇 |
2012年 | 6830篇 |
2011年 | 6767篇 |
2010年 | 4358篇 |
2009年 | 3977篇 |
2008年 | 5685篇 |
2007年 | 5693篇 |
2006年 | 5474篇 |
2005年 | 5230篇 |
2004年 | 5115篇 |
2003年 | 4883篇 |
2002年 | 4615篇 |
2001年 | 1085篇 |
2000年 | 846篇 |
1999年 | 1141篇 |
1998年 | 1303篇 |
1997年 | 904篇 |
1996年 | 819篇 |
1995年 | 716篇 |
1994年 | 685篇 |
1993年 | 728篇 |
1992年 | 679篇 |
1991年 | 653篇 |
1990年 | 610篇 |
1989年 | 527篇 |
1988年 | 557篇 |
1987年 | 459篇 |
1986年 | 443篇 |
1985年 | 538篇 |
1984年 | 624篇 |
1983年 | 525篇 |
1982年 | 597篇 |
1981年 | 566篇 |
1980年 | 494篇 |
1979年 | 408篇 |
1978年 | 410篇 |
1977年 | 355篇 |
1976年 | 334篇 |
1975年 | 291篇 |
1974年 | 326篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
111.
Intact protoplasts are ruptured by rapid centrifugation through a narrow-aperture nylon mesh and the intact chloroplasts are then separated from the cytoplasm by sedimentation through a layer of silicone oil below the mesh. Within 6 to 8 s of starting the centrifuge, 90% of the chloroplasts are separated into the pellet fraction which contains only 10 to 15% contamination by mitochondria and peroxisomes and less than 5% contamination by soluble cytoplasm as judged by the distribution of marker enzymes. This technique should allow determination of the distribution of metabolites between the chloroplast and cytoplasmic compartments of intact protoplasts. 相似文献
112.
113.
Competition for sulphur in a grass-clover association 总被引:2,自引:0,他引:2
Summary A 3 × 3 factorial experiment with nitrogen and sulphur fertilizers was carried out on a grass-clover association in an area where there is little if any cyclic return of sulphur. In the absence of sulphur, grass took up 98 per cent of the total uptake of sulphur, and nitrogen fixation by associated clover was negligible. In the absence of fertilizer nitrogen, dressings of sulphur as gypsum stimulated clover growth; at a low rate of application of sulphur, nitrogen fertilizer increased grass growth and clover was suppressed. This suppression was largely overcome with a higher dressing of sulphur. Sulphur therefore must be added to the group of elements (phosphorus, nitrogen and potassium) for which grass may compete intensely when grown with clover and when nitrogen fertilizers are applied to a grass-clover association adequate supplies of sulphur must be assured in order to minimise suppression of clover. Sulphate of ammonia may stimulate clover growth under these conditions. Solubility of gypsum was low in a dry season and residual effects were pronounced. 相似文献
114.
The Escherichia coli dnaW mutation is an allele of the adk gene 总被引:3,自引:0,他引:3
Joan M. Henson Aleksandra Blinkowa James R. Walker 《Molecular & general genetics : MGG》1982,186(4):488-492
Summary A dnaW mutant, isolated on the basis of inability to effect conjugal DNA transfer at high temperature, has been shown by complementation and enzyme assay to be defective in the adk (adenylate kinase; EC 2.7.4.3) locus. The adk mutant, known to have reduced ATP concentration at the nonpermissive temperature (Cousin and Belaich 1966), was used to demonstrate a donor energy requirement for stable aggregate formation and for chromosome transfer in conjugation. 相似文献
115.
Michael E. Salvucci Archie R. Portis Jr. William L. Ogren 《Photosynthesis research》1985,7(2):193-201
Ribulosebisphosphate carboxylase/oxygenase (EC 4.1.1.39) (rubisco) must be fully activated in order to catalyze the maximum rates of photosynthesis observed in plants. Activation of the isolated enzyme occurs spontaneously, but conditions required to observe full activation are inconsistent with those known to occur in illuminated chloroplasts. Genetic studies with a nutant of Arabidopsis
thaliana incapable of activating rubisco linked two chloroplast polypeptides to the activation process in vivo. Using a reconstituted light activation system, it was possible to demonstrate the participation of a chloroplast protein in rubisco activation. These results indicate that a specific chloroplast enzyme, rubisco activase, catalyzes the activation of rubisco in vivo. 相似文献
116.
Stephen J. Traphagen Michael J. Dimarco Margaret E. Silliker 《RNA (New York, N.Y.)》2010,16(4):828-838
Regions of the Didymium iridis mitochondrial genome were identified with similarity to typical mitochondrial genes; however, these regions contained numerous stop codons. We used RT-PCR and DNA sequencing to determine whether, through RNA editing, these regions were transcribed into mRNAs that could encode functional proteins. Ten putative gene regions were examined: atp1, atp6, atp8, atp9, cox1, cox2, cytb, nad4L, nad6, and nad7. The cDNA sequences of each gene could encode a functional mitochondrial protein that was highly conserved compared with homologous genes. The type of editing events and editing sequence features were very similar to those observed in the homologous genes of Physarum polycephalum, though the actual editing locations showed a variable degree of conservation. Edited sites were compared with encoded sites in D. iridis and P. polycephalum for all 10 genes. Edited sequence for a portion of the cox1 gene was available for six myxomycetes, which, when compared, showed a high degree of conservation at the protein level. Different types of editing events showed varying degrees of site conservation with C-to-U base changes being the least conserved. Several aspects of single C insertion editing events led to the preferential creation of hydrophobic amino acid codons that may help to minimize adverse effects on the resulting protein structure. 相似文献
117.
118.
119.
120.